Dysfunction of the vascular endothelium is a hallmark of most conditions that are associated with atherosclerosis and is therefore held to be an early feature in atherogenesis. However, the mechanisms by which endothelial dysfunction occurs in smoking, dyslipidaemia, hyperhomocysteinaemia, diabetes mellitus, arterial hypertension, cerebrovascular diseases, coronary artery disease and heart failure are complex and heterogeneous. Recent data indicate that endothelial dysfunction is often associated with erectile dysfunction, which can precede and predict cardiovascular disease in men. This paper will provide a concise overview of the mechanisms causing endothelial dysfunction in the different cardiovascular risk factors and disease conditions, and of the impact of the intervention measures and treatments.